Certain beverage or food preparation machines use capsules containing ingredients to be extracted or to be dissolved; for other machines, the ingredients are stored and dosed automatically in the machine or else are added at the time of preparation of the drink.
Most coffee machines possess filling means that include a pump for liquid, usually water, which pumps the liquid from a source of water that is cold or indeed heated through heating means, such as a heating resistor, a thermoblock or the like.
Most beverage machines have a reservoir for containing and for the supply of a constituent of the beverage to be prepared, usually a liquid constituent such as water. However, other constituents may be contained in such reservoirs, in particular liquid concentrates or solid material such as coffee beans or ground coffee, etc.
Some of these machines include a level detector for detecting the level of the content in the reservoir and prevent any process using such a content when insufficient for carrying out the process and/or signalling to the user such a low level.
For instance, DE 102 01 768 discloses a beverage machine with a reservoir for containing a liquid and a detector for detecting a minimum level of fill. The reservoir has a wall with an angled protruding two-part section or corner at the minimum level of fill. The level detector includes a light emitter and a light detector arranged on either side of this two part section. Light emitted by the emitter extends via a first part of this angled section into the reservoir cavity and, when the light passes through air instead of this liquid i.e. after the liquid has reached the minimum level in the reservoir, the emitted light exits through the second part of this angled section to hit the detector. JP 2000-329609 discloses a similar optical level detector for sensing a level of syrup in a reservoir of a vending machine. In both disclosures, the emitter and detector are located adjacent each side of an angled section or corner of the reservoir, the level of fill of which is to be detected. A problem with these embodiments resides in the fact that the emitter and detector are located on different faces of the reservoir which complicates the arrangement of the light emitter and detector and connections thereof to a control unit, in particular to a printed circuit board whose shape will normally not follow the shape of the angled section or corner about which emitter and detector are placed.
Another solution is disclosed in U.S. Pat. No. 7,017,408, in which a beverage maker has a housing with a lid element that is movable against the mouth of a liquid container. The lid element includes a light emitter and a light detector, the emitter emitting onto the surface of the liquid an inclined light beam that is reflect onto the detector when the liquid is at a certain level. A problem with this approach resides in the fact that the emitter and detector are mounted in a movable component of the beverage maker, which involves complications with the connection between the emitter, detector and the fixed control unit of the beverage maker. Moreover, such a emitter-detector arrangement operating with a reflection on the liquid surface can hardly be located anywhere else than above the surface which also increases the complexity of the connections of the emitter-detector to a control unit.
GB 1 553 642 discloses an embodiment of a liquid level detector having a light emitter and a light detector mounted into the base of a triangular refractor. This refractor further includes two converging planes which are opposite the emitter and detector and which are fitted into the cavity of a reservoir for containing a liquid. When the level of liquid is below the refractor, light emitted by the emitter inside the refractor is substantially reflected by the facing angled planes into the detector. Conversely, when the level of liquid is above the refractor, i.e. the converging planes are immersed in the liquid, the light emitted by the emitter being substantially refracted through the converging planes into the liquid instead of being reflected back into the detector. A problem with this embodiment lies in the fact that the triangular refractor protrudes into the liquid in the reservoir and is directly exposed thereto and thus requires occasional cleaning, including for removing scale deposits. Moreover, this triangular refractor protruding inside the cavity of the reservoir i.e. rendering the cavity of the reservoir non-convex, complicates the cleaning of such cavity. FR 2 672 390 discloses a similar level detector in which the triangular refractor is located in a lid of a container of a household apparatus, such as an air conditioner. Thus, improvements in these type devices are desired.